1. Field of the Invention
The present invention relates to a method of and apparatus for increasing the strength of a gear tooth, particularly the fatigue strength at the root or root fillet thereof.
2. Description of the Prior Art
With a view to increasing the strength of a gear tooth, particularly the fatigue strength at the root or root fillet at which the gear tooth is most likely to be broken due to fatigue, shot peening has heretofore been used for processing the gear tooth after heat treatment.
Shot peening is a process for casting or blowing metal particles upon the gear tooth to harden the surface thereof while causing residual compressive stress in the surface layer, and is widely used for increasing the fatigue strength or tensile strength of mechanical parts or elements such as a toothed wheel, spring, shaft, etc.
Shot peening however has the disadvantage that the area to be shot peened is limited due to the restrictions of the shot peening device, such as the restriction on nozzle bore size. For this reason, the metal particles are liable to be cast or blown upon portions other than the tooth bottom and root fillet of the gear tooth such as the tooth face and tooth flank, causing the problem that the tooth face and tooth flank become rough or have undesirable protrusions or recessions.